Systems comprising an internal combustion engine in combination with an air or gas compressor, of the so-called monoblock design, have been in existence for a number of years. The monoblock design utilizes a basic internal combustion engine and converts a number of the cylinders for gas compression. The remaining cylinders drive the device or vehicle. For example, one typical application is for a V-8 engine in which a four of the eight cylinders are configured to engage components of an gas compressor.
In a typical arrangement, the compressor block will be mounted over certain cylinders and the standard engine piston replaced with a specially configured compressor piston. Systems of this type are described in U.S. Pat. Nos. 3,462,074 and 4,232,997. In early monoblock designs, the conversion was limited to single stage compressors operating in the range of 100-125 psi. More recently, higher pressure and multi-stage compressors have been developed using the monoblock concept. These multi-stage or high pressure air compressors have produced new problems due to the high pressure forces involved.
In a typical engine set up, the piston is engaged to the connecting rod by way of a piston pin. The piston pin and connecting rod are configured to allow lubricating oil to enter the loading area between the pin, the piston and the connecting rod. The need for oil at the piston pin and rod assembly is clear--i.e., to prevent premature wear, galling and friction failures. In a typical 4 cycle engine, the load exerted on the piston pin and rod assembly reverses as the piston reaches and passes top dead center and bottom dead center during its cycle. This load reversal is essential in allowing lubricating oil to flow all around the piston pin and rod assembly.
In high pressure or multi-stage compressor systems, the high cylinder pressures at the gas compressor cylinders create high forces that do not permit the load reversals in the piston pin and rod assembly, In other words, the high pressure constantly pushes toward the crankshaft of the engine regardless of whether the piston has passed top dead center in its cycle. With typical piston pin and rod assemblies, the results are friction failures and premature wear and galling of the piston pin assembly.
One way to address this problem is to use frictionless bearings, such as roller and ball bearing assemblies. However, the ball bearing assemblies are generally more expensive and more complicated than the typical piston pin and rod assembly. Perhaps more significantly, the roller and ball bearing assemblies require greater space within the engine for their installation than is required by a piston pin assembly. With a focus on smaller and lighter engines, engine block designers are loathe to increase the otherwise limited space available for these bearing components.
The present invention addresses this problem of the use of high pressure or multi-stage compressors in a monoblock design. In particular, the present invention permits the use of the typical piston pin and rod assembly while allowing for adequate lubrication throughout the entire assembly.
Another aspect of the present invention addresses a means for providing supercharged air to the internal combustion engine component of the monoblock combination. In the past, separate engine driven superchargers have been used to provide higher pressure air to the engine, thereby improving performance and engine efficiency. The separate superchargers add weight and require additional space, an approach often disfavored in the design of engines for use in a monoblock engine/gas compressor combination. Nevertheless, the use of certain engine cylinders for gas compression rather than power frequently necessitates some supercharging capability to maintain performance. One aspect of the present invention provides such supercharging without the penalty of significant additional weight or space requirements.
The present invention further contemplates that the internal combustion engine run on natural gas fuel. Most engines experience some form of blow-by in which the combustion mixture within the cylinders leaks past the pistons into the crankcase. For natural gas engines, collected air/natural gas mixture in the crankcase can be a volatile mixture in the right proportions. There is therefore a need for some safety dictated mechanism for preventing the risk of inadvertent combustion of this air/gas mixture in the engine crankcase. Another aspect of the present invention fulfills this need.